Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for a television broadcast camera, a video camera, a digital still camera, a silver-halide film camera, and so on.
Description of the Related Art
In recent years, a compact zoom lens having a large aperture ratio (large F-number) and a large zoom ratio, and achieving high optical performance has been demanded for an image pickup apparatus such as a television camera, a silver-halide film camera, a digital still camera, and a video camera. As a general zoom lens having a large aperture ratio and a large zoom ratio, there has been known a positive-lead type four-unit zoom lens including four lens units as a whole, in which the lens unit disposed closest to an object has a positive refractive power. This four-unit zoom lens is known to have a configuration in which a first lens unit for focusing, a second lens unit having a negative refractive power for zooming, a third lens unit for correcting image plane variations due to zooming, and a fourth lens unit having a positive refractive power for image formation are arranged in this order from the object side to the image side.
For example, in Japanese Patent No. 4469625, a first lens unit is divided into a first negative lens sub-unit G11, a second positive lens sub-unit G12, and a third positive lens sub-unit G13, which are arranged in this order from the object side. Japanese Patent No. 4469625 proposes an inner-focus type zoom lens that performs focusing by moving the second positive lens sub-unit G12 on the optical axis.
With resolution enhancement of pixels of an image pickup element, there has been a demand for high optical performance over all the zoom range and all the focus range. In order for the aforementioned positive-lead type zoom lens to achieve both a reduction in size and high optical performance, it is necessary to appropriately set the refractive powers of the respective lenses and the lens configuration, particularly the power arrangement and the lens configuration in the first lens unit.
According to Japanese Patent No. 4469625, the first lens unit is provided with an increased number of lenses to enhance the design latitude for aberration correction so that the zoom lens can achieve higher performance. The first lens unit, however, includes the lenses having large effective diameters, and accordingly the increase in the number of lenses in the first lens unit entails an increase in the weight of the entire product.